I'm In Hot Water

This is my hot water tank. There are many others like it, but this one is mine.

It's in year 11 of its 6 year warranty, and has finally decided to give up the ghost. However, it did not do this by springing a leak. No, instead it decided to start backfiring out the venturi tube.

So, let's pull out the burner and see what's up.

This is what's known as an ultra-low-NOx burner. Usually the venturi tube would mix a slightly rich mixture of natural gas and air, squirt that into a burner, and the mixture would exit through a series of small ports, which is where it would burn. The gas would mix with the ambient air in the burner chamber, leading to a fuel-lean mixture at the outside of the flame and a fuel-rich mixture on the inside. A little bit of NOx and a little bit of unburned HC would be created, respectively, and exit out the flue.

These emissions were considered not entirely ideal, so California enacted some regulations clamping down on the limits for NOx and HC, which required a redesign of the combustion system. Now, instead of injecting a fuel rich mixture, a stoichiometric mixture is created, and fed up through a screen where a sheet of flame burns in an otherwise sealed combustion chamber. This results in a much more even fuel-air mixture throughout the entire flame, with (in theory) no lean spots to produce NOx and no rich spots to produce unburned HC emissions.

And this is all fine and dandy until the screen cakes up with grime and holes get burned into it.

These holes, in particular, are what allow the flame front to pass back through the screen and up the venturi tube, causing the backfiring that I observed.

Now I didn't much fancy the idea of not having hot water, so my first attempt to remedy this situation was to get out the wire brush and clean the grime off the screen to see if that would fix things.

The screen cleaned up nicely, improving the gas flow, but the holes still present meant that the flame was not able to be confined to the combustion chamber.

A new burner assembly would have been roughly $300, but given the age of the tank, I'd like to introduce you to its replacement.

It's a like-for-like swap, a 40gal gas heater, which even comes straight from the factory pre-scuffed.

Well this is off to a great start but whatever, its job isn't to look pretty, it just needs to heat water and not set my car hole on fire.

Step one of the replacement is draining the old tank. I initially started off by hooking this garden hose to the drain spigot, but it was not flowing especially quickly.

40 gallons is only 8 buckets, so that's what I tried next.

That seemed to be working well enough, so I busied myself with disconnecting the tank from the gas, water, and oddly excessive earthquake strapping.

Then roughly 8 buckets of hot water later, we pop the new one into place, hooking things up in the reverse order that it was removed.

Now you might be wondering how, exactly, I managed to remove the old tank and put the new one in its place all by myself?

The answer is simple: Grab hold of it, tilt it back so it's well balanced on top of you, and then lift with your knees. It's only 130lbs empty, just man up and do it.

After I did the swap, my curiosity got the best of me: I wondered just what an 11 year old anode would look like. The answer?

Some anode material is technically still there.

Which is the best kind of still there.

I actually suspect there was a bit more material than this still clinging to the anode rod, but I had used my impact wrench to remove it and at one point the rod got spun at quite a high rate of speed, which is why it's rather bent looking. I'm sure some anode fragments were probably flung off during this process.

Anyway, the entire ordeal started at approximately 8:30pm and, including a 30 minute round trip to the Home Despot, I had everything buttoned up and running again at 11:00pm. So disaster was averted and I was able to have a hot shower at the usual time before tucking into bed.